We propose to continue our researches into certain effects of lead on mammalian kidneys, namely (1) stimulation of cell proliferation in the proximal convoluted tubules, and its possible significance for carcinogenesis, (2) induction of the synthesis of a specific acidic protein in renal tubular epithelial cells by small doses of lead and its possible significance as a detoxifying agent, and (3) the possibility that lead can act as an initiator of carcinogenesis in various sorts of cells.